A Brief History of Element Discovery, Synthesis, and AnalysisWatson, Glen W.
History
A Brief History of Element Discovery, Synthesis, and Analysis
Watson, Glen W.
Chemical elements; Chemistry -- History; Transuranium elements -- Synthesis
The next two elements, einsteinium ({99}Es) and fermium ({100}Fm), were
originally found in the debris from the thermonuclear device "Mike,"
which was detonated on Eniwetok atoll November 1952. (This method of
creating new substances is somewhat more extravagant than the mythical
Chinese method of burning down a building to get a roast pig.)
These elements have since been made in nuclear reactors and by
bombardment. This time the "bullet" was N<14> stripped of electrons till it
had a charge of +6, and the target was plutonium.
Researchers at the University of California used new techniques in
forming and identifying element 101, mendelevium. A very thin layer of
{99}Es<253> was electroplated onto a thin gold foil and was then bombarded,
from behind the layer, with 41-MeV [alpha] particles. Unchanged {99}Es<253>
stayed on the gold, but those atoms hit by [alpha] particles were
knocked off and deposited on a "catcher" gold foil, which was then
dissolved and analyzed (Fig. 3). This freed the new element from most of
the very reactive parent substances, so that analysis was easier. Even
so, the radioactivity was so weak that the new element was identified
"one atom at a time"; this is possible because its daughter element,
fermium, spontaneously fissions and releases energy in greater bursts
than any possible contaminant.
[Illustration: Fig. 3. The production of mendelevium.]
In 1957, in Stockholm, element 102 was reported found by an
international team of scientists (who called it nobelium), but diligent
and extensive research failed to duplicate the Stockholm findings.
However, a still newer technique developed at Berkeley showed the
footprints--if not the living presence--of 102 (see Fig. 4). The rare
isotope curium-246 is coated on a small piece of nickel foil, enclosed
in a helium-filled container, and placed in the heavy-ion linear
accelerator (Hilac) beam. Positively charged atoms of element 102 are
knocked off the foil by the beam, which is of carbon-12 or carbon-13
nuclei, and are deposited on a negatively charged conveyor apron. But
element 102 doesn't live long enough to be actually measured. As it
decays, its daughter product, {100}Fm<250>, is attracted onto a charged
aluminum foil where it can be analyzed. The researchers have decided
that the hen really did come first: they have the egg; therefore the hen
must have existed. By measuring the time distance between target and
daughter product, they figure that the hen-mother (element 102) must
have a half-life of three seconds.
[Illustration: Fig. 4. The experimental arrangement used in the
discovery of element 102.]
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